The present invention relates to a semiconductor memory device, and more particularly a method of manufacturing a semiconductor memory device using a photoresist pattern formed by an argon fluoride (ArF) laser or a fluorine (F2) laser as a light source.
In the semiconductor memory device fabrication processes, photolithography is used to form patterns on a substrate with various materials. A photoresist, which is generally organic film forming polymers, is coated on a target layer, and exposed with a mask to induce photo-reaction in the photoresist, selectively. Then, the photoresist is developed and predetermined photoresist patterns are obtained. The photoresist patterns are mainly used as etch barriers during etching the target layer.
The photolithography has been moved ahead grew by leaps and bounds, from the beginning of mass production of dynamic random access memory (DRAM) which is representative of the semiconductor memory device.
The development of photolithography has been accomplished by the development in the every filed of an exposing system, a photoresist material, a mask and a process. The advent of a lens having high numerical aperture and an alignment device in the field of the exposing, a chemically amplified resist (CAR) in field of the photoresist material, a phase shift mask and an optical proximity correction in the field of the mask and method using a tri-layer-resist, a bi-layer-resist, a top-surface-imaging and an anti-reflection-coating in the field of the process, serve as good example, respectively.
The initial exposure equipment is a contact printer, where a mask is directly contacted with a substrate and aligned by an operator who looks directly at the mask and the substrate with the naked eye. The contact printer had been developed to reduce the gap between the mask and substrate, and a proximity printer is developed. The proximity printer classified into a soft contact and a hard contact according to the amount of the gap.
In the photolithography, the resolution is inverse proportion to wavelength of the light source. The early stepper adopting step and repeat method, the wavelength of light source has been shortened from 436 nm, i. e. g-line, to 365 nm, i.e. i-line. A stepper and another exposing system, such as a scanner type exposing device, using a deep ultra violet(DUV), for example, 248 nm of KrF excimer laser, have been developed.
Photoresist patterns of which critical dimension(CD) are not more than 0.15 xcexcm can be formed owing to the developments of an exposing device, photoresist material and other techniques used in the photolithography process.
It can be expected to form photoresist patterns of which CD are not more than 0.11 xcexcm by using a deep ultra violet(DUV), i.e. 193 nm of KrF excimer laser.
In case of using the DUV, the resolution and the depth of focus (DOF) are improved compared to the case of using i-line. However, it is difficult to control process conditions. In the photolithography using the DUV, the difficulties are caused by an optical problem owing to use of light source having short wavelength and a chemical problem owing to the use of the CAR. As the wavelength become shorter, the effect of CD swing becomes a serious problem because of the effect of standing wave. The effect of CD swing is a phenomenon of periodic variation of line width of the photoresist pattern, and the effect of CD swing is caused by the variation of the extent of interference between incident light and reflective light, which varies by a trifle thickness difference of the photoresist film or the sub-layer. In the photolithography process using the DUV as the light source, the CAR should be used to improve sensitivity, however the problems of the stability of post exposure delay (PED) and the dependence on the sub-layer are generated owing to the reaction mechanism of the CAR.
The main problem of the lithography using the ArF laser as a light source is a development of new photoresist material. The photoresist for the ArF laser is also one kind of CAR, as the photoresist for the KrF, however the benzene rings should not be contained in the photoresist for ArF laser. The benzene rings have been used for improving barrier characteristic of the photoresist for i-line and KrF laser in the dry etching. In case that the benzene rings are in the photoresist for ArF laser, the absorption rate increases in the 193 nm, which is the wavelength of the ArF laser, that is, the transparent rate decrease, accordingly, it is difficult to expose the photoresist to the bottom thereof. Therefore, it is need to develop a photoresist having high barrier characteristic without the benzene rings.
However, a photoresist having a CycloOlefin-Maleic Anhydride (COMA), a photoresist having Acrylate species and a photoresist containing both the COMA and the Acrylate species, which have been used for ArF laser, have the benzene rings therein.
Accordingly, in case of forming photoresist patterns by exposing the photoresist, in which the benzene rings are contained, with the ArF laser, the deformation or lumping of the photoresist patterns is generated when an etch process using fluorine-based gas as an etching gas is carried out.
Therefore, it is need to supplement the physical characteristic of the photoresist pattern, in which the benzene rings are contained and formed by exposing with the ArF laser, in order to improve barrier characteristic of the photoresist patterns in the etch process using the fluorine-based gas.
It is, therefore, an object of the present invention to provide a method for manufacturing a semiconductor memory device using a photoresist pattern formed by an argon fluoride (ArF) laser as a light source.
In accordance with an aspect of the present invention, there is a provided a method for manufacturing a semiconductor memory device, comprising the steps of: a) forming a mask layer on a target layer to be etched; b) coating a photoresist on the mask layer; c) exposing the photoresist by using a light resource whose wavelength is of about 157 nm to 193 nm; d) forming a photoresist pattern by developing the photoresist; e) forming a mask pattern by selectively etching the mask layer with an etching gas except fluorine-based gases by using the photoresist pattern as an etching mask; and f) selectively etching the target layer by using the mask pattern as an etching mask.
In accordance with another aspect of the present invention, there is provided a method for manufacturing a semiconductor memory device, comprising the steps of: a) forming a mask layer on an interlayer insulating layer overlying a semiconductor substrate; b) coating a photoresist on the mask layer; c) exposing the photoresist by using a light resource whose wavelength is of about 157 nm to about 193 nm; e) forming a photoresist pattern by developing the photoresist; f) forming a mask pattern by selectively etching the mask layer with an etching gas except a fluorine-based gas by using the photoresist pattern as an etching mask; g) forming a contact hole exposing the semiconductor substrate by selectively etching the interlayer insulating layer by using the mask pattern as an etching mask; h) forming a conductive layer on the interlayer insulating layer including the contact hole; and i) forming a plug by etching the conductive layer and the mask pattern until the interlayer insulating layer is exposed as the conductive remains only in the contact hole.